Aluminum is a metal which offers a good compromise between electrical conductivity, mechanical strength, weight and cost. As such, the use of aluminum wire or cable as an electrical conductor has increased significantly in recent years. However, there are many possible applications where aluminum wire or cable may be used only if certain physical and mechanical properties are achieved. These include, for example, utility cable, building wire, telephone cables, battery cables, automotive harness wiring, aircraft cables, transformer wire, magnet wires and appliance cords.
Aluminum conductors, in commercial practice, are commonly produced by drawing down an aluminum or aluminum alloy rod in a so-called drawbench having a succession of dies through which the rod is drawn under tension to achieve a progressive reduction in diameter. At the exit end of the drawbench, the wire is wound onto a winding form, e.g. a basket, reel, spool or bobbin. The wire wound on the winding form is either shipped directly to customers, or proceeds to other equipment for further processing, for example, a wire stranding plant for manufacturing a conductor cable. The aluminum cable is also mostly wound or coiled on a winding form before being shipped to customers.
It is, in many cases, required that the aluminum conductor coiled on a spool be heat-treated (e.g. annealed) in order to provide certain mechanical and physical properties for further processing or to achieve desirable properties in the final product. When the aluminum conductor is heat-treated while coiled or wound on the form, especially when heat treated in a high temperature furnace and/or for a long period of time, the individual wire strands in close contact with each other are likely to stick together or to the centre or sides of the form. This may be due, for example, to intermetallic diffusion occurring in the contact zone or one wire pulling over the dry surface of another wire. This leaves markings on the surface of the conductor, or causes the wire to “hang-up” (stick or catch to itself) during unwinding, resulting in “catching” or wire breakage. These markings and/or the effects caused by the “catching” incidents are referred to as “heat treating damage.” This heat treating damage reduces the commercial value of the conductor and possibly its performance. This damage is particularly significant when the heat treatment is the last step on the process before supplying the wire or cable to the customers.
Conventionally, to solve the above problems, i.e, to prevent heat treating damage, oils, silicones, stearates, and waxes, etc., have been used to provide some degree of lubricity to the coiled strands throughout the heat treatment process. At times, oils are sprayed onto or flushed through the coiled wire or cable to minimize the damage. These prior art techniques reduce, but do not eliminate, the metal to metal damage when wire products are wound and unwound from a winding form, particularly at temperatures above about 260° C. The materials used for lubrication must be carefully selected to minimize staining or corrosion of the aluminum itself. Further, these prior art materials, such as oil, silicone, stearate and wax, create an environmental, fire or explosion hazard.
There is, therefore, a need to overcome the difficulties of the prior art procedures and to prevent or minimize heat treating damage of bare aluminum conductors, such as wire or cable.